Health

How Sodium Levels Affect Your Exercise Performance

Are you getting enough—or too much—sodium?

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Consuming a sodium-rich beverage one to two hours before exercise can be an effective method of increasing body water stores. Under the right circumstances, this can stave off dehydration and theoretically allow you to get away with consuming less fluid during exercise. However, a separate issue is whether sodium ingestion during exercise influences performance. Several studies have assessed whether sodium ingestion during exercise delays fatigue or improves how fast athletes finish a race. The bad news is that sodium supplementation has, for the most part, elicited few positive performance effects.

In one example, 114 competitors of the Cape Town Ironman triathlon ingested either sodium chloride or placebo tablets during the race; despite consuming an average of about 3.5 grams of sodium, the sodium chloride group didn’t fare better in comparison to the placebo group when it came to finishing time, core body temperature, or body mass changes. In another study, nine cyclists completed two 72-kilometer time trials over hilly terrain in New Zealand; one trial was done while ingesting 0.7 grams of sodium chloride per hour, and the other was done while ingesting a placebo. The athletes drank as much fluid as they wished, and despite the fact that sodium supplementation led to greater thirst, more fluid consumption, and better maintenance of blood volume than placebo, performance wasn’t different between the interventions. A final example comes from a study that supplemented athletes with 1.8 grams of sodium or cornstarch during treadmill running or cycling. After two hours of exercising at a moderate intensity, treadmill grade or cycling power was increased every minute until the athletes threw in the towel. Each athlete completed two trials while ingesting each treatment, and in the end, none of the outcomes (temperature change, thermal sensation, body weight change, or performance) were influenced by sodium.

In contrast to these three studies, one 2016 experiment did show a possible improvement in half-Ironman triathlon performance when researchers assigned 26 participants to either electrolyte capsules (containing sodium, chloride, potassium, and magnesium) or a placebo. In the end, the electrolyte group finished about 26 minutes (roughly 7.8 percent) faster than the placebo group. While this seems impressive, the sample size was quite small for this type of study (meaning the results are less trustworthy), and because the electrolyte supplement also contained several compounds other than sodium, the benefits could have been from one of these other ingredients.

If supplementing with sodium during exercise likely doesn’t impact real-world performance, then why is it included in most sports beverages in moderate amounts (200–600 milligrams per liter)? To be sure, some research does show that including sodium in a beverage confers slight physiological advantages (e.g., maintenance of plasma volume and serum osmolality). These are just the kinds of findings that excite geeky sports scientists making electrolyte drinks, but ultimately, they probably don’t translate to tangible benefits on the racecourse or field. Another reason sodium is added to these beverages is that it stimulates the drive to drink; most hydration scientists used to believe that more was better when it came to fluid ingestion, even though today we recognize that’s often not the case. And last but not least, beverage makers also don’t mind it when athletes drink more of their products (for obvious financial reasons), and sodium is one of several ingredients that can increase consumption of said products.

I want to be clear that it is important for some athletes to up the sodium content of their diets in order to replace losses through sweating. Athletes can lose several grams or more of sodium each day if they have large total sweat volumes, and for these athletes the standard amount of dietary sodium probably isn’t enough. However, this lost sodium can easily be replaced by eating sodium-rich foods and beverages throughout the day. (Hooray for those salted Saltines, eh?) That’s not to say that consuming an electrolyte-containing drink during exercise is a poor choice; instead, I’m saying athletes shouldn’t expect to improve their performance by consuming sodium during exercise itself.

After cutting through the hype, the data underpinning the supposed benefits of sodium supplementation during exercise are quite weak. While some studies show that body weight, blood volume, and blood sodium levels are slightly better maintained with sodium supplementation, these physiological changes haven’t consistently translated into meaningful performance advantages. That being said, ingesting a sodium-rich beverage before exercise is a potentially viable strategy for enhancing endurance performance in hot/humid conditions, especially when fluid availability is limited during competition.

Sodium and Cramping

If you’ve ever experienced a muscle cramp during a race or game, you probably know that the pain can be excruciating. In some cases, it seems as if an invisible force is tightening the muscle beyond what is possible through human will. Marathon spectators can plop themselves around mile 20 and watch as dozens of runners pass by as they try, sometimes in vain, to work out the cramps in their legs. Muscle cramps in cyclists and swimmers are also fairly common and can even be dangerous if they hit suddenly and unexpectedly. While quite rare, occasionally a swimmer will drown after suffering from a muscle cramp that they can’t relieve.

Strategies for preventing exercise-associated muscle cramps include making sure you taper your training volume going into competition and—for endurance races, specifically—that you don’t start out of the gate too fast. Still, muscle cramps can hit even the best prepared athletes, and at that point, many turn to stretching and massage. Beyond these mechanical remedies, athletes, coaches, and practitioners often believe that dehydration and electrolyte imbalances are leading causes of exercise-associated muscle cramps. This widespread belief has grown out of media reports and a few observational studies, such as an investigation that showed five footballers who had a history of cramps lost twice as much sodium in their sweat during a training camp as teammates with no history of cramping.

Initially, these correlational studies gave credence to the hypothesis that electrolyte imbalances play a role in exercise-associated muscle cramps. As such, foods and beverages rich in electrolytes have been regularly consumed by athletes seeking relief from muscle cramps. One sodium-rich beverage, pickle juice, has received an inordinate amount of attention as a surefire way to alleviate cramps. In one well-documented instance, the 2000 Philadelphia Eagles supposedly fought off muscle cramps in 100°F conditions by using pickle juice and, in the process, defeated the cramp-laden Dallas Cowboys. (This has since been dubbed the “Pickle Juice Game.”) Considering the abundance of these sorts of media reports in the early 2000s, it isn’t surprising that by 2008 up to one quarter of athletic trainers were using pickle juice to treat muscle cramps.

Despite the hype, studies on pickle juice and muscle cramping are few and far between. In one well-controlled experiment, however, ingestion of pickle juice did actually curtail cramping as compared to ingesting water. Researcher Kevin Miller and his colleagues had participants exercise until they lost 3 percent of their body mass through sweating, after which toe muscle cramps were induced through electrical stimulation of the tibial nerve. The average cramp duration with water ingestion was 134 seconds, which was reduced by 37 percent with pickle juice. Although this finding would at first glance lend weight to sodium’s effectiveness as a cramp reliever, the fluids were ingested immediately after the cramps were induced, meaning there wasn’t enough time for the sodium to be absorbed and carried through the participants’ bloodstreams to directly impact their cramping muscles.

What, then, could explain pickle juice’s positive influence in this study? One leading hypothesis is that something in the pickle juice other than sodium stimulates receptors in the mouth and gut that, when activated, affect signaling between the nervous system and skeletal muscles. If not sodium, what ingredient in pickle juice could be doing this? Our current best guess is that the vinegar in pickle juice is responsible for these cramp-relieving effects. Specifically, vinegar is believed to activate receptors in the mouth and upper gut that quiet the neurons that send signals to your muscles. This is likely why athletes and athletic trainers often describe pickle juice as having a rapid onset of action; it doesn’t need to be digested and absorbed to work.

Subsequent studies have revealed that other food ingredients activate these same receptors (referred to scientifically as transient receptor potential [TRP] vanilloids and ankyrins). Ginger, cinnamon, mustard, and chili peppers have all been identified as activators of these receptors, and in a promising series of studies, ingesting mixtures of these types of ingredients reduced muscle cramp severity and cramp thresholds.

Before you go into a state of muscle cramp–relieving ecstasy, be aware that the improvements in these studies were of modest magnitude, so you shouldn’t expect to completely prevent all muscle cramps with the use of pickle juice or other TRP activators. Even so, with these scientific developments, we’re beginning to learn that the old anecdotes about pickle juice and muscle cramping are partially true. However, the common belief that sodium is responsible for these benefits is probably unfounded.


Adapted from The Athlete’s Gut by Patrick Wilson with permission of VeloPress.

The Athlete’s Gut